The idea was to cast aluminium at 1000°C in a wodden mold. The expect result was that the wooden mold would slightly burn giving shape to a new mold.
Instead of using aluminium which is too hot and too problematic to handle, tin has been selected. The meltin point of tin is 250°C. The challenge was to find a material with a burning point close to this temperature. After many trials, polyurethane foam as been the best matter.